These studies may be relevant to the problem of human psychotic illness. The dopamine hypothesis has not been fully tested in man for the wide range of neuropsychiatric disorders where abnormalities in dopamine metabolism may play a role. We may be able to decide which CSF and plasma measures (HVA, GABA, cAMP) reflect specific regional central dopamine metabolism. If plasma HVA measures truly reflect changes in central dopamine turnover then greater access to clinical populations will be provided.